ok bit of an update, I've identified which part is the control solenoid, it's this silver box on the bulk head



When I first ran the engine it pulled the flap shut at idle and put the MIL on

Then I turned off the engine, disconnected the battery, had a brew, came back reconnected everything, fired her up and the light had gone out. went for a drive, upto temperature, light stayed off.

Turned off the car, waited 1 min, restarted, light came back on!
AGGHHHHHHHHHHHHH!!

What decides when to open/close these flaps? Is it something simple like a switch that could be at fault? Dont really want to have to buy a new valve thingy from ford, bet it's v. v. expensive.